1. Field of the Invention
This invention relates to curable silicone compositions which give cured products especially excellent in hydrophilic properties.
2. Description of the Prior Art
Curable silicone compositions are excellent in the properties of cured products thereof, and are used widely for printing plates for lithography, mold release agents, adhesives, paints, sealants, reflecting sheets, dental impression materials, etc. As the impression material, particularly, addition-curing type curable silicone compositions are generally used. The addition-curing type curable silicone compositions have good curability, and are advantageous in that the compositions are cured with very little shrinkage and with no by-products. Furthermore, the cured products of the compositions of this type have excellent properties such as good dimensional stability, tastelessness and odorlessness, easy demoldability, etc.
Because the conventional curable silicone compositions are hydrophobic, however, it has been difficult to take an accurate impression of a wet surface by use of the compositions, because of the poor affinity of the compositions for the surface. For instance, when the conventional curable silicone composition is used as a dental impression material to take an impression of an inside part of a wet oral cavity, it is difficult to obtain a precise impression of detailed parts. In addition, when a model is formed by casting a plaster slurry in to the impression thus obtained, there arises a problem that the wettability of the impression with the plaster slurry is poor, making it difficult to obtain an accurate model.
In view of the above difficulties, curable silicone compositions improved in hydrophilicity by incorporating a nonionic surface active agent therein have been proposed [Lacy, A., Treleaven, S. & Tendresen, M., Cal. Dent. Assn. J., 5, 36-40 (1977); Norling, D. K. & Reisbicd, M. H., J. Pros. Dent., 42, 342-347 (1979)]. Also, U.S. Pat. Nos. 4,657,959 and 4,752,633 and Japanese Pre-examination Patent Publication (KOKAI) No. 252706/1987 propose curable silicone compositions in which a hydrophilicity-imparting agent comprising a silicone-modified polyether compound has been added.
The curable silicone composition comprising a nonionic surface active agent must contain a large amount of the nonionic surface active agent in order to improve satisfactorily the wettability of the cured composition by a plaster slurry. If the nonionic surface active agent is added in a large amount, however, the curing reaction of the composition is hindered, and the resultant cured product has poorer physical properties, such as an increased permanent set.
The curable silicone composition comprising a silicone-modified polyether compound, also, are inevitably accompanied by the problem of lowered physical properties of the cured products.